The possibility of using fiber optic sensors in geo-technical measurements is investigated with the aim of improving measurement performances of parameters which are of geo-technical interest and which can be indirectly measured starting from geo-technical probe strain data. This work refers to the use of real geo-technical probes and particular attention has been paid to the flat dilatometer, in order to evaluate the effect on measurement performances (resolution, sensitivity, accuracy) of using fiber optic sensors with respect to traditional ones. Design methodology is described in order to detect solutions able to improve not only measurement accuracy, but also resolution and reliability. In particular the effect of sensor position, size and installation has been studied by means of a theoretical and experimental study.
Preliminary tests are discussed, which allowed to experimentally verify the system behaviour and which have been carried out on a test rig specifically designed and set-up.
In this paper a methodology is described to be implemented in a simple and low cost automatic measuring apparatus for on line measurement of Cr(VI) concentration in water, which is able to be controlled by a PC and to be inserted in an integrated environmental control multi-sensor network. Measuring section is a miniaturized fiber optic probe, whose working principle is light absorption of the complex Chromium (VI) - Diphenylcarbazide. Device design and set up guidelines of an automatic measuring device are described in order to get a reliable, effective and user friendly configuration and to reduce measurement uncertainty depending on interfering quantities of different type, fluid dynamic, optical, environmental, taking into account "in situ" measuring conditions.
A simple experimental test bench is described for the measurement of eccentricity of fiber optic connectors for telecommunications applications. The measuring principle is based on the detection of the track of the light beam exiting from the fiber optic tip by means of a 2D position sensing detector. Displacement due to fiber eccentricity, which is in the order of a few micrometers can be optically amplified by lenses in order to improve eccentricity measurement uncertainty. Optomechanical and electrical solutions which have been used in order to reduce the global measurement uncertainty and the effect of many interfering quantities has been deeply studied form both a theoretical and experimental point of view. Finally some operating consideration is also discussed.
In this paper the experimental characterization of a transducer for on line measurement of coating thickness in food industry applications is described, which is composed by a fiber optic probe and by an eddy-current proximity one. The method is based on measuring reflectance by a fiber optic probe of the coating plated on thin steel sheets. The eddy current proximity probe should be used to measure the substrate position. In order to evaluate the feasibility of this approach, a particular attention has been paid to the accuracy of the method, since an accuracy in the order of plus or minus 1 micrometer should be achieved for practical interest. With this aim, the effect of the main interfering and modifying quantities of geometrical (sensor size, probe head angle of incidence, working distance, ...) and optical (light source and photo-detector behavior stability, ...) type has been evaluated both theoretically and experimentally by using a calibration test bench in stationary working conditions. Furthermore, a calibration test bench has been built, where a translating and vibrating steel plate is realized, in order to evaluate the effect of translation velocity of the plate and also of cross vibrations. Results of dynamic calibration are also described and discussed, in order to get information about the final sensor configuration.
Some aspects concerning the calibration procedure are shown for a fiber optic sensor to be used for on-line chromium (VI) concentration measurements. The sensor is based on the measurement of light absorption of a sampling volume between transmitting and receiving optics, made by means of GRIN lenses for sensor size miniaturizing purposes. In particular, the geometrical design of the probe has been discussed, together with the effects of optical and mechanical solutions. These have been set in the probe, referring to the measuring performances to be achieved and, in particular measuring range, sensitivity, accuracy and time stability. The results of preliminary experimental analysis are also described, which allowed validation of the design indication and getting information for probe development.
Some aspects concerning a methodology for the measurement of thickness of dry and wet coatings which is based on a fiber optic probe are discussed in order to verify the feasibility of this approach and the capability of such a probe of on- line measuring. In this preliminary step of the research some problems discussed mainly concerning the methodology which has been proposed and which is based on the measuring of the reflectance of the coating plated on thin steel sheets for use in the food industry. Furthermore the effect of the main interfering and modifying quantities is discussed both theoretically and experimentally when the measurement has to be carried out in order to allow on-line coating thickness measurements with satisfactory accuracy.
In this paper possible ways of increasing the signal to noise ratio of a laser Doppler vibrometer with fiber optic components are discussed, in order to improve its metrological characteristics and to enlarge its field of possible industrial applications. System improvements, related to the frequency shifting block of the vibrometer, to its photodetector stage and to the optical head, which recovers the light scattered by a vibrating target, have been experimentally evaluated. It must be noticed that this activity has been carried out taking into account the requirement of simplicity and handiness of the measurement system and using solutions from both an optical and an electronic point of view, which are inexpensive as much as possible.
An experimental comparison has been carried out between two laser Doppler vibrometers, different as for frequency shift generation between measuring and reference beam of the interferometer. In particular, two systems, based either on a Bragg cell or on a rotating diffraction grating for frequency shifting, have been compared, with reference to both metrological and operating behavior. Based on the analysis of experimental information, a quantitative evaluation has been carried out of the effect on either optical configuration of the most typical operative parameters to be taken into account in laser Doppler vibrometry, in order to define the best optical lay-out and configuration depending on the specific industrial application.
A laser Doppler vibrometer prototype has been designed in order to get a simple and relatively inexpensive architecture of both the optical part of the system and the signal analysis electronics. In order to improve its operating performances fiber optic components have also been used. The metrological characteristics (measuring range, accuracy, signal to noise ratio, resolution, etc.) of the vibrometer have been evaluated by means of experimental results, comparing them with high performance commercial vibrometers. Some guidelines to develop the system for field applications are also discussed.
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